Download Family Letter 8

CHAPTER
8
Family Letter
Section A
What We Are Learning
Dear Family,
Lines and Angles
In this section, your child will be learning the necessary
terminology for understanding and applying the concepts of
geometry. When given a figure, your child will be able to
identify points, segments, rays, lines, and planes. Use the
chart to review of these basic concepts.
Vocabulary
These are the math words
we are learning:
acute angle an angle that
measures less than 90°
adjacent angles angles
with a common endpoint
and side, but no common
interior points
Concept
Definition
Point
An exact location in space.
Line
line a set of points that
extends without end in
opposite directions
A
Ray
A
Line Segment
A
Plane
AB
B
A set of points that forms
a flat surface that extends
forever.
A
C
plane ABC
B
Your child will also learn that congruent figures are figures that
have the same shape and the same size. Congruent line
segments are segments that are the same length. Congruent
sides and segments are marked with an equal number of
tick marks.
Identify the line segments that are congruent.
plane a set of points that
forms a perfectly flat
surface that extends
forever
A
WZ
BC
AC YZ
W
one tick mark
two tick marks
Y
B
Copyright © by Holt, Rinehart and Winston.
All rights reserved.
AB
B
A part of a line with two
endpoints.
obtuse angle an angle
whose measure is greater
than 90° but less than
180°
perpendicular lines lines
that intersect to form right
angles
B
Part of a line that has one
endpoint and extends forever.
line segment a part of a
line with two endpoints
parallel lines lines that
are in the same plane and
never intersect
AB
A set of points that extends
without end in opposite
directions.
congruent having the
same size and shape
congruent angles angles
that have the same
measure
point P
P
angle two rays with a
common endpoint
complementary angles
two angles whose
measures add to 90°
Symbols
C
Z
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Holt Mathematics
CHAPTER
8
Family Letter
Section A, continued
point an exact location in
a plane
ray a part of a line that
has one endpoint and
extends forever
Another geometric concept your child will be learning involves
angles and angle relationships. Your child will recognize and
classify angles into four different categories: acute, obtuse,
right, and straight.
right angle an angle that
measures exactly 90°
skew lines lines that lie
in different planes. They
are neither intersecting nor
parallel
straight angle an angle
that measures exactly
180°
supplementary angles
two angles whose
measures have a sum of
180°
Acute
90°
Obtuse
90°
Right
90°
Straight
180°
Lines also have special relationships. Intersecting lines that
form right angles are called perpendicular lines. Lines that
are in the same plane, but do not cross, are called parallel
lines. If two parallel lines are cut by a third line, or a
transversal, all of the acute angles are congruent and all of
the obtuse angles are congruent. Lines that are not in the
same plane and never intersect are called skew lines.
transversal a line that
intersects two or more
lines
vertex the common
endpoint formed by two
rays
vertical angles a pair of
opposite congruent angles
formed by intersecting
lines
Perpendicular Lines
Parallel Lines
Parallel Lines
cut by a transversal
The information covered in this section will provide a strong
foundation for the geometric concepts and applications your
child will be using throughout this chapter and future
mathematics courses.
Sincerely,
Copyright © by Holt, Rinehart and Winston.
All rights reserved.
62
Holt Mathematics
Name
CHAPTER
8
Date
Class
Family Letter
Lines and Angles
Use geometry notation to identify the figures.
D
F
C
A
E
1. points
B
2. lines
3. rays
Tell whether each angle is acute, right, obtuse, or straight.
4.
5.
6.
Use the figure to the right for Exercises 7–11.
7. Name one pair of complementary angles.
E
B
8. Name two pairs of supplementary angles.
P
50°
90°
G
H
140°
D
Tell the measure of each angle.
9. PGB
10. DGH
11. EGH
Find the measures of 1 and 3.
12. m1
13. m3
135° 1
3
3. Possible answer: AF
, AD
, AE
, AB
, FB
Answers: 1. A, B, C, D, E, F 2. Possible answer: ED
4. straight 5. obtuse 6. acute 7. BGP and PGD 8. DGB and BGE, EGH and HGD 9. 50°
10. 140° 11. 40° 12. 45° 13. 45°
Copyright © by Holt, Rinehart and Winston.
All rights reserved.
63
Holt Mathematics
Name
CHAPTER
8
Date
Class
Family Fun
Geometric Baseball
Materials
1 number cube
Vocabulary words from this chapter
Marker pieces
Directions
• Split into two teams.
• The person “batting”
tells what you “hit”.
1 – a single
2 – a double
3 – a triple
rolls the number cube. The number on the cube
4 – a home run
5 – strike
6 – out
• In order to get on base, you must correctly define a geometry term. If
you do not define the word correctly, it is an out. The more words your
team correctly defines, the better chance you have to move your team
around the bases. The words may come from anywhere in this chapter.
• After 3 outs, the teams switch places.
• The team with the most runs after 5 innings wins the game.
Scoreboard
Team 1
Team 2
2
3
1
H
Copyright © by Holt, Rinehart and Winston.
All rights reserved.
64
Holt Mathematics